By Kim Deok-hyun SINGAPORE, June 5 (Yonhap) -- South Korea is seeking the strongest U.N. resolution against North Korea for its torpedo attack on one of its warships in March, its defense chief said Saturday, acknowledging that more efforts will be needed to win support from U.N. Security Council members.

"As for us, we will be making efforts to bring out the strongest resolution," Defense Minister Kim Tae-young told reporters after attending a security forum here. South Korea officially referred the North to the Security Council earlier Saturday over the March 26 sinking of its warship Cheonan.

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The U.N. referral is the first step in what is expected to be an arduous process to condemn and punish Pyongyang for the provocation. North Korea denies any involvement in the sinking and has threatened an "all-out war" against any such attempts.

The North is already under a series of U.N. sanctions for its nuclear and missile tests last year.

Kim acknowledged that South Korea needs to make more efforts.

"Things cannot be done solely by our government. We need the resolution of the Security Council members," Kim said. "We will be taking such factors into consideration."

But its diplomatic campaign at the U.N. has been complicated by China and Russia, two of the five permanent members of the Council that can veto any sanctions or other harsh measures on North Korea. Both close allies of Pyongyang, the two countries have yet to accept the probe results accusing North Korea.

Kim met bilaterally with Ma Xiaotian, deputy chief of staff of China's People's Liberation Army, on the sidelines of the security forum.

"I explained to him fully for over 30 minutes what caused the Cheonan incident, what surfaced in the process of the investigation," Kim said. "China remains cautious, but we hope that it will reach a responsible conclusion."

South Korea has announced a package of retaliatory measures against its communist neighbor after a team of multinational investigators concluded last month that the Cheonan was downed by a torpedo fired by a stealthy North Korean submarine that sneaked into South's waters.

Seoul said it was cutting off exchanges and trade with North Korea while resuming its propaganda warfare across the heavily fortified border, ending 10 years of an inter-Korean reconciliatory mood under predecessor governments.

A large-scale joint naval drill with the United States was initially scheduled for next week as a show of force against North Korea, but it was delayed by two weeks to give the U.S. more time for preparations.

Some observers speculated that the two countries postponed the drill to buy time for diplomacy at the U.N., or that they were softening their response against the North. Kim dismissed the speculations, emphasizing that the sides needed more time to make the drill more "meaningful." "It's not a delay, but an adjustment of the schedule to make the drill more systematic and meaningful," he said.

The defense chief said this year's security forum was an opportunity to make known North Korea's provocative behavior and win international support for Seoul's position.

Kim held a flurry of bilateral talks with his counterparts at the annual forum, commonly known as the Shangri-La Dialogue, including U.S. Defense Secretary Robert Gates and Japanese Defense Minister Toshimi Kitazawa.